Underground pipelines are commonly used to carry oil, natural gas and other fluids. If a leak develops in the pipeline, at best this will result in the loss of some of the fluid being transported. More likely, however, the leak may present an increasing environmental hazard, and the leak may become more severe with time. Further, more catastrophically, a pipeline may rupture. A rupture, particularly of a natural gas pipeline, can cause an explosion and fire. Obviously, it is therefore preferable to identify the location of a potential leak or rupture so that the compromised portion of the pipeline may be repaired or replaced. A variety of pipeline inspection tools exist for this purpose, some of which inspect the pipeline as they pass through it. A tool that passes through the pipeline to inspect it is often referred to in the industry as a pig. A pig may have magnets which create flux lines along the axis of the pipe. Disturbances in the flux density as the tool moves through the pipe can then be interpreted to determine if these disturbances are indicative of a compromised section of pipeline.
A drawback with a tool that creates axial flux lines is that it will not detect axially directed cracks or flaws. To address this drawback, some tools employ one or more additional magnets, each additional magnet providing transversely directed flux lines. However, this modified tool suffers the drawback that the flux sensors between the poles of each of these additional magnets are each exposed to different flux densities, which reduces the accuracy of the measurements.
Therefore, there is a need for an improved pipeline inspection tool.